Switching between different firebase projects (runtime) in one single APK file

We are integrating firebase messaging in our android application for push notifications. We are going to use SNS from server side to send push message to firebase. Below is our use case:

• We have three servers: QA, STG and PRODUCTION
• We created say three projects in firebase console: say appQA, appSTG and appProd
• But we want to generate only 1 single APK which can receive firebase push notification from any of the above three fire base projects depending on the server to which our user logs-in.
• We configured each project in firebase and at end we got 1 google-services.json file per project (total 3)
• Now how do we configure or generate 1 APK which can encompass all three json files and switch between them runtime and not build-time because we do not want to build separate APKs for separate environments. We have a strict requirement of generating one single APK that can be used to connect to all our environments and receive push notifications from all environments.
• We have tried flavors and build types but both are build-time and not run-time

This is first time that we are venturing in world of push notifications on android.

PS: The obvious solution is to just have one project in firebase and configure it on client and all of our servers can use the same project but ideally we want separate project for Production vs QA/STG

If you really need a single APK that somehow self-selects which Firebase project it works against, you can't use the automatic init provided by the Gradle plugin.

Normally, Firebase apps init automatically (definitely read my blog post there) via data injected by the gradle plugin. This system works in a vast majority of cases, but not in yours.

If the normal case doesn't work for you, you'll have to disable the FirebaseInitProvider via Android build tools (see tools:node="remove"), and initialize your app yourself with FirebaseApp.initializeApp() with a FirebaseOptions that you construct. You need to arrange for the init to happen before any APIs are called, or you'll get errors.